This project will continue to study children with leukemia and other chromosomal disorders, as well as their first, second, and third degree relatives when available. In this way, it will be determined whether skin tissue cultures derived from these individuals have markers that might indicate the degree of leukemia risk. The markers will continue to include the degree of transformed foci in tissue culture from such individuals as determined by SV40 virus transformation and correlated with T-Antigen formation in the transformed cells. Fibroblast cultures from skin biopsies from leukemic children, their relatives, from individuals without malignancies (controls), and from other individuals have been developed. In these studies, attempts to determine whether there is a correlation between the degree of cell transformation in cultured cells, cytogenetic instability and the incidence of leukemia in the children will be determined. As soon as a sufficient number of transformation studies have been carried out that can be correlated with the cultures that have been developed, the relationship to the occurrence of leukemia will be determined.